The protozoan parasite Jrypanosoma brucei is the causative agent of African sleeping sickness, a disease that is invariably fatal without treatment. T. brucei has served as a model system for the study of the related trypanosomatid pathogens Trypanosoma cruzi and Leishmania spp., and the three together infect over 20 million people worldwide. Leishmania has been a significant pathogen affecting American military personnel in the Middle East. The absence of vaccines and the toxic nature of drugs that combat these diseases, particularly sleeping sickness, make research into new drug and vaccine targets imperative. With the release of the genome sequences of all three trypanosomatids, we now face important decisions as to which of many targets to pursue. We have chosen to examine protein kinases and phosphatases since they are likely to be of major biological significance. Having identified all of the protein kinases in the genome through informatic studies, we will now identify all of the protein phosphatases. We also will examine the pattern of expression of protein kinases and phosphatases at the mRNA level. We are particularly interested identifying those molecules whose expression peaks in actively cycling cells in the bloodstream (human- infective) stage and those that may function as receptor kinases. We plan to pursue in more depth those molecules whose human homologues have served as drug targets for chronic diseases, including MAP kinase kinases and protein tyrosine phosphatases. Function will be approached through localization studies and RNAi knockdowns, as well as analysis of potential substrates. Together these studies will signficantly expand our knowledge of the network of signaling interactions in trypanosomes, with the goal of identifying new drug and vaccine targets.